Tuesday, November 23, 2010

Following a study of what is in effect a miniature galaxy buried inside a normal-sized one – like a Russian doll – astronomers using a CSIRO telescope have concluded that massive black holes are more powerful than we thought.

An international team of astronomers led by Dr Manfred Pakull at the University of Strasbourg in France has discovered a ‘microquasar’ – a small black hole, weighing only as much as a star, that shoots jets of radio-emitting particles into space.

Called S26, the black hole sits inside a regular galaxy called NGC 7793, which is 13M light-years away in the Southern constellation of Sculptor.

Earlier this year Pakull and colleagues observed S26 with optical and X-ray telescopes (the European Southern Observatory’s Very Large Telescope and NASA’s Chandra space telescope).

Now they have made new observations with CSIRO’s Compact Array radio telescope near Narrabri, NSW. These show that S26 is a near-perfect analogue of the much larger ‘radio galaxies’ and ‘radio quasars’.

Powerful radio galaxies and quasars are almost extinct today, but they dominated the early Universe, billions of years ago, like cosmic dinosaurs. They contain big black holes, billions of times more massive than the Sun, and shoot out huge radio jets that can stretch millions of light-years into space.

Astronomers have been working for decades to understand how these black holes form their giant jets, and how much of the black hole’s energy those jets transmit to the gas they travel through. That gas is the raw material for forming stars, and the effects of jets on star-formation have been hotly debated.

"Measuring the power of black hole jets, and therefore their heating effect, is usually very difficult," said co-author Roberto Soria (University College London), who carried out the radio observations.

"With this unusual object, a bonsai radio quasar in our own backyard, we have a unique opportunity to study the energetics of the jets."

Using their combined optical, X-ray and radio data, the scientists were able to determine how much of the jet’s energy went into heating the gas around it, and how much went into making the jet glow at radio wavelengths.

They concluded that only about a thousandth of the energy went into creating the radio glow.

"This suggests that in bigger galaxies too the jets are about a thousand times more powerful than we’d estimate from their radio glow alone," said Dr Tasso Tzioumis of CSIRO Astronomy and Space Science.

"That means that black hole jets can be both more powerful and more efficient than we thought, and that their heating effect on the galaxies they live in can be stronger."

The study was made possible by a recent upgrade to the Compact Array, which can now do work of this kind five times faster than before.

Blinking numbers on a liquid-crystal display (LCD) often indicate that a device's clock needs resetting. But in the laboratory of Zhong Lin Wang at Georgia Institute of Technology, the blinking number on a small LCD signals the success of a five-year effort to power conventional electronic devices with nanoscale generators that harvest mechanical energy from the environment using an array of tiny nanowires.

In this case, the mechanical energy comes from compressing a nanogenerator between two fingers, but it could also come from a heartbeat, the pounding of a hiker's shoe on a trail, the rustling of a shirt, or the vibration of a heavy machine. While these nanogenerators will never produce large amounts of electricity for conventional purposes, they could be used to power nanoscale and microscale devices -- and even to recharge pacemakers or iPods.

Wang's nanogenerators rely on the piezoelectric effect seen in crystalline materials such as zinc oxide, in which an electric charge potential is created when structures made from the material are flexed or compressed. By capturing and combining the charges from millions of these nanoscale zinc oxide wires, Wang and his research team can produce as much as three volts -- and up to 300 nanoamps.

"By simplifying our design, making it more robust and integrating the contributions from many more nanowires, we have successfully boosted the output of our nanogenerator enough to drive devices such as commercial liquid-crystal displays, light-emitting diodes and laser diodes," said Wang, a Regents' professor in Georgia Tech's School of Materials Science and Engineering. "If we can sustain this rate of improvement, we will reach some true applications in healthcare devices, personal electronics, or environmental monitoring."

Recent improvements in the nanogenerators, including a simpler fabrication technique, were reported online in the journal Nano Letters. Earlier papers in the same journal and in Nature Communications reported other advances for the work, which has been supported by the Defense Advanced Research Projects Agency (DARPA), the U.S. Department of Energy, the U.S. Air Force, and the National Science Foundation (NSF).

"We are interested in very small devices that can be used in applications such as health care, environmental monitoring and personal electronics," said Wang. "How to power these devices is a critical issue."

The earliest zinc oxide nanogenerators used arrays of nanowires grown on a rigid substrate and topped with a metal electrode. Later versions embedded both ends of the nanowires in polymer and produced power by simple flexing. Regardless of the configuration, the devices required careful growth of the nanowire arrays and painstaking assembly.

In the latest paper, Wang and his group members Youfan Hu, Yan Zhang, Chen Xu, Guang Zhu and Zetang Li reported on much simpler fabrication techniques. First, they grew arrays of a new type of nanowire that has a conical shape. These wires were cut from their growth substrate and placed into an alcohol solution.

The solution containing the nanowires was then dripped onto a thin metal electrode and a sheet of flexible polymer film. After the alcohol was allowed to dry, another layer was created. Multiple nanowire/polymer layers were built up into a kind of composite, using a process that Wang believes could be scaled up to industrial production.

When flexed, these nanowire sandwiches -- which are about two centimeters by 1.5 centimeters -- generated enough power to drive a commercial display borrowed from a pocket calculator.

Wang says the nanogenerators are now close to producing enough current for a self-powered system that might monitor the environment for a toxic gas, for instance, then broadcast a warning. The system would include capacitors able to store up the small charges until enough power was available to send out a burst of data.

While even the current nanogenerator output remains below the level required for such devices as iPods or cardiac pacemakers, Wang believes those levels will be reached within three to five years. The current nanogenerator, he notes, is nearly 100 times more powerful than what his group had developed just a year ago.

Writing in a separate paper published in October in the journal Nature Communications, group members Sheng Xu, Benjamin J. Hansen and Wang reported on a new technique for fabricating piezoelectric nanowires from lead zirconate titanate -- also known as PZT. The material is already used industrially, but is difficult to grow because it requires temperatures of 650 degrees Celsius.

In the paper, Wang's team reported the first chemical epitaxial growth of vertically-aligned single-crystal nanowire arrays of PZT on a variety of conductive and non-conductive substrates. They used a process known as hydrothermal decomposition, which took place at just 230 degrees Celsius.

With a rectifying circuit to convert alternating current to direct current, the researchers used the PZT nanogenerators to power a commercial laser diode, demonstrating an alternative materials system for Wang's nanogenerator family. "This allows us the flexibility of choosing the best material and process for the given need, although the performance of PZT is not as good as zinc oxide for power generation," he explained.

And in another paper published in Nano Letters, Wang and group members Guang Zhu, Rusen Yang and Sihong Wang reported on yet another advance boosting nanogenerator output. Their approach, called "scalable sweeping printing," includes a two-step process of (1) transferring vertically-aligned zinc oxide nanowires to a polymer receiving substrate to form horizontal arrays and (2) applying parallel strip electrodes to connect all of the nanowires together.

Using a single layer of this structure, the researchers produced an open-circuit voltage of 2.03 volts and a peak output power density of approximately 11 milliwatts per cubic centimeter.

"From when we got started in 2005 until today, we have dramatically improved the output of our nanogenerators," Wang noted. "We are within the range of what's needed. If we can drive these small components, I believe we will be able to power small systems in the near future. In the next five years, I hope to see this move into application."

A University of Colorado at Boulder-led study shows that specific types of stem cells transplanted into the leg muscles of mice prevented the loss of muscle function and mass that normally occurs with aging, a finding with potential uses in treating humans with chronic, degenerative muscle diseases.

The experiments showed that when young host mice with limb muscle injuries were injected with muscle stem cells from young donor mice, the cells not only repaired the injury within days, they caused the treated muscle to double in mass and sustain itself through the lifetime of the transplanted mice. "This was a very exciting and unexpected result," said Professor Bradley Olwin of CU-Boulder's molecular, cellular and developmental biology department, the study's corresponding author.

Muscle stem cells are found within populations of "satellite" cells located between muscle fibers and surrounding connective tissue and are responsible for the repair and maintenance of skeletal muscles, said Olwin. The researchers transplanted between 10 and 50 stem cells along with attached myofibers -- which are individual skeletal muscle cells -- from the donor mice into the host mice.

"We found that the transplanted stem cells are permanently altered and reduce the aging of the transplanted muscle, maintaining strength and mass," said Olwin.

A paper on the subject was published in the Nov. 10 issue of Science Translational Medicine. Co-authors on the study included former CU-Boulder postdoctoral fellow John K. Hall, now at the University of Washington Medical School in Seattle, as well as Glen Banks and Jeffrey Chamberlain of the University of Washington Medical School.

Olwin said the new findings, while intriguing, are only the first in discovering how such research might someday be applicable to human health. "With further research we may one day be able to greatly resist the loss of muscle mass, size and strength in humans that accompanies aging, as well as chronic degenerative diseases like muscular dystrophy."

Stem cells are distinguished by their ability to renew themselves through cell division and differentiate into specialized cell types. In healthy skeletal muscle tissue, the population of satellite stem cells is constantly maintained, said Olwin.

"In this study, the hallmarks we see with the aging of muscles just weren't occurring," said Olwin. "The transplanted material seemed to kick the stem cells to a high gear for self-renewal, essentially taking over the production of muscle cells. But the team found that when transplanted stem cells and associated myofibers were injected to healthy mouse limb muscles, there was no discernable evidence for muscle mass growth.

"The environment that the stem cells are injected into is very important, because when it tells the cells there is an injury, they respond in a unique way," he said. "We don't yet know why the cells we transplanted are not responding to the environment around them in the way that the cells that are already there respond. It's fascinating, and something we need to understand."

At the onset of the experiments the research team thought the increase in muscle mass of the transplanted mice with injured legs would dissipate within a few months. Instead, the cells underwent a 50 percent increase in mass and a 170 percent increase in size and remained elevated through the lifetime of the mice -- roughly two years, said Olwin.

In the experiments, stem cells and myofibers were removed from three-month-old mice, briefly cultured and then transplanted into three-month-old mice that had temporarily induced leg muscle injuries produced by barium chloride injections. "When the muscles were examined two years later, we found the procedure permanently changed the transplanted cells, making them resistant to the aging process in the muscle," he said.

"This suggests a tremendous expansion of those stem cells after transplantation," Olwin said. Fortunately, the research team saw no increase in tumors in the transplanted mice despite the rapid, increased growth and production of muscle stem cells.

As part of the research effort, the team used green fluorescent protein -- which glows under ultraviolet light -- to flag donor cells in the injected mice. The experiment indicated many of the transplanted cells were repeatedly fused to myofibers, and that there was a large increase in the number of satellite cells in the host mice.

"We expected the cells to go in, repopulate and repair damaged muscle and to dissipate," Olwin said. "It was quite surprising when they did not.

"It is our hope that we can someday identify small molecules or combinations of small molecules that could be applied to endogenous muscle stem cells of humans to mimic the behavior of transplanted cells," Olwin said. "This would remove the need for cell transplants altogether, reducing the risk and complexity of treatments."

But Olwin said it is important to remember that the team did not transplant young cells into old muscles, but rather transplanted young cells into young muscles.

The research has implications for a number of human diseases, Olwin said. In muscular dystrophy, for example, there is a loss of a protein called dystrophin that causes the muscle to literally tear itself apart and cannot be repaired without cell-based intervention. Although injected cells will repair the muscle fibers, maintaining the muscle fibers requires additional cell injections, he said.

"Progressive muscle loss occurs in a number of neuromuscular diseases and in muscular dystrophies," he said. "Augmenting a patient's muscle regenerative process could have a significant impact on aging and diseases, improving the quality of life and possibly improving mobility."

Olwin said the research team is beginning experiments to see if transplanting muscle stem cells from humans or large animals into mice will have the same effects as those observed in the recent mouse experiments. "If those experiments produce positive results, it would suggest that transplanting human muscle stem cells is feasible," he said.

The research was funded in part by the National Institutes of Health and the Muscular Dystrophy Association.

Depression appears to be associated with a molecular-level disturbance in the body’s 24-hour clock, new research suggests.

Scientists examined genes that regulate circadian rhythm in people with and without a history of depression. As a group, those with a history of depression had a higher level of activity of the so-called Clock gene, which has a role in regulating circadian rhythm, than did people with no mood disorders.

Higher expression levels of this gene suggest something is amiss in the body’s 24-hour biological and behavioral cycle, which could affect sleep patterns and other physiological functions governed by circadian rhythm. Sleep disturbance is a common symptom of depression.

“If we look at people who have depression, they can have very different groups of symptoms. So if some of them have a biological profile that shows circadian dysfunction, there is a chance that a circadian type of treatment might be more helpful for them than for others.”

But the researchers noted that the association between the gene activity and depression is just that – a link, with no demonstrated causal effect in either direction. At this point in what is known about the relationship, this genetic profile could lead to depression or depression could alter this particular gene function, or some other biological or environmental influences could combine to disrupt the circadian clock.

Though this study offers just a snapshot in time of circadian activity in people with and without depression, the finding could have important clinical implications if it is supported by additional research. People with depression who share this genetic profile might benefit most from sleep-related treatments, such as light therapy or a class of antidepressants that act on melatonin, a hormone that regulates sleep.

“We know that there are a lot of insomnia symptoms in depression, especially early morning awakening,” said Jean-Philippe Gouin, a graduate student in psychology at Ohio State University and lead author of the study. “We can’t say with this study that there is a direct relationship between this altered gene function and behavior, but the research suggests that over-expression of circadian genes might serve as a biomarker of vulnerability to depression.”

The research is published in a recent issue of the Journal of Affective Disorders.

Gouin is currently serving a predoctoral clinical psychology internship at Rush University Medical Center. As a graduate student at Ohio State, he has worked for years on studies led by the Institute for Behavioral Medicine Research that examine the health effects of chronic stress in people who take care of loved ones with dementia. Some of the people who participated in this study were from that population.

“There was some evidence that chronic stress led to changes in circadian gene expression in animals,” Gouin said. “We wanted to see if that would be the case in humans, and one of the models of chronic stress in humans is dementia caregiving stress. We found that caregiving was not related to circadian genes, but instead it was really the history of depression that distinguishes between regulation of these genes.”

The researchers collected blood samples from, and conducted interviews with, 60 people: 25 who were providing at least five hours of care per week for a family member with dementia and 35 non-caregiving controls with similar demographic characteristics. Thirty participants had a lifetime history of depression, while the other 30 had never been clinically depressed.

All blood samples were drawn between 9 a.m. and 11 a.m. to control for variations in circadian clock gene activity that occur throughout the day.

The researchers analyzed the blood to determine the messenger RNA levels for four circadian genes, including Clock. Messenger RNA (mRNA) contains the set of instructions for building proteins, so its level in genes dictates how much protein each gene is making.

As a group, the participants with a history of depression had a significantly higher level of Clock mRNA expression than did participants who had never been depressed. The researchers didn’t find statistically significant results for the other three genes.

The association between depression and elevated Clock mRNA levels held up even when figures were adjusted for differences in age, sex, body mass index, alcohol and tobacco use, exercise, other medical conditions and caregiving status, Gouin noted.

He said that to further define the relationship between this genetic profile and depression, researchers ideally would monitor research participants over time to measure the changes in mRNA expression in circadian genes through a 24-hour cycle.

“If we look at people who have depression, they can have very different groups of symptoms. So if some of them have a biological profile that shows circadian dysfunction, there is a chance that a circadian type of treatment might be more helpful for them than for others,” Gouin said.

A team of astronomers has found evidence that the universe may have gone through a warming trend early in its history. They measured the temperature of the gas that lies in between galaxies, and found a clear indication that it had increased steadily over the period from when the universe was one tenth to one quarter of its current age. This cosmic climate change is most likely caused by the huge amount of energy output from young, active galaxies during this epoch. The researchers publish their results in a forthcoming paper in the journal Monthly Notices of the Royal Astronomical Society.

"Early in the history of the universe, the vast majority of matter was not in stars or galaxies", University of Cambridge astronomer George Becker explains. "Instead, it was spread out in a very thin gas that filled up all of space." The team, led by Becker, was able to measure the temperature of this gas using the light from distant objects called quasars. "The gas, which lies between us and the quasar, adds a series of imprints to the light from these extremely bright objects," Becker continues, "and by analyzing how those imprints partly block the background light from the quasars, we can infer many of the properties of the absorbing gas, such as where it is, what it's made of, and what its temperature is."

The quasar light the astronomers were studying was more than ten billion years old by the time it reached Earth, and had travelled through vast tracts of the universe. Each intergalactic gas cloud the light passed through during this journey left its own mark, and the accumulated effect can be used as a fossil record of temperature in the early universe. "Just as Earth's climate can be studied from ice cores and tree rings," says Becker, "the quasar light contains a record of the climate history of the cosmos.

'Of course, the temperatures we measured are a bit different from what you find on Earth," commented Becker. "One billion years after the Big Bang, the gas we measured was a 'cool' 8,000 degrees Celsius. By three and a half billion years the temperature had climbed to at least 12,000 degrees Celsius."

The warming trend is believed to run counter to normal cosmic climate patterns. Normally the universe is expected to cool down over time. As the cosmos expands, the gas should get colder, much like gas escaping from an aerosol can. To create the observed rise in temperature, something substantial must have been heating the gas.

"The likely culprits in this intergalactic warming are the quasars themselves", explains fellow team member Martin Haehnelt, who is also at Cambridge University's newly-established Kavli Institute for Cosmology. "Over the period of cosmic history studied by the team, quasars were becoming much more common. These objects, which are thought to be giant black holes swallowing up material in the centres of galaxies, emit huge amounts of energetic ultraviolet light. These UV rays would have interacted with the intergalactic gas, creating the rise in temperature we observed."

One of the lightest and most abundant elements in these intergalactic clouds, helium, played a vital role in the heating process. Ultraviolet light stripped the electrons from a helium atom, freeing the electrons to collide with other atoms and heat up the gas. Once the supply of fresh helium was exhausted, the universe started to cool down again. Astronomers believe this probably occurred after the cosmos was one quarter of its present age.

The team's discovery was made possible by data taken with the 10-meter Keck telescopes in Hawaii, aided by advanced simulations run on a supercomputer at the University of Cambridge. Along with Becker and Haehnelt, the team included James Bolton at the University of Melbourne, and Wallace Sargent at the California Institute of Technology.

U of T scientists have found that chemicals used to line junk food wrappers and microwave popcorn bags are migrating into food and being ingested by people where they are contributing to chemical contamination observed in blood.

Perfluorinated carboxylic acids or PFCAs are the breakdown products of chemicals used to make non-stick and water- and stain-repellant products ranging from kitchen pans to clothing to food packaging. PFCAs, the best known of which is perfluorooctanoic acid (PFOA), are found in humans all around the world.

“We suspected that a major source of human PFCA exposure may be the consumption and metabolism of polyfluoroalkyl phosphate esters or PAPs,” said Jessica D’eon, a graduate student in the Department of Chemistry. “PAPs are applied as greaseproofing agents to paper food contact packaging such as fast food wrappers and microwave popcorn bags.”

In the U of T study, rats were exposed to PAPs either orally or by injection and monitored for a three-week period to track the concentrations of the PAPs and PFCA metabolites, including PFOA, in their blood. Human exposure to PAPs had already been established by the scientists in a previous study. Researchers used the PAP concentrations previously observed in human blood together with the PAP and PFCA concentrations observed in the rats to calculate human PFOA exposure from PAP metabolism.

“We found the concentrations of PFOA from PAP metabolism to be significant and concluded that the metabolism of PAPs could be a major source of human exposure to PFOA, as well as other PFCAs,” said Professor Scott Mabury of chemistry, lead researcher of the study.

“This discovery is important because we would like to control human chemical exposure but this is only possible if we understand the source of this exposure. In addition, some try to locate the blame for human exposure on environmental contamination that resulted from past chemical use rather than the chemicals that are currently in production.

“In this study we clearly demonstrate that the current use of PAPs in food contact applications does result in human exposure to PFCAs, including PFOA. We cannot tell whether PAPs are the sole source of human PFOA exposure or even the most important, but we can say unequivocally that PAPs are a source and the evidence from this study suggests this could be significant.”

Regulatory interest in human exposure to PAPs has been growing. Governments in Canada, the United States and Europe have signalled their intentions to begin extensive and longer term monitoring programs for these chemicals. The results of this investigation provide valuable additional information to such regulatory bodies to inform policy regarding the use of PAPs in food contact applications.